but even in TC1,
what would prevent me from simply refund and issue a new ticket if the whole ticket has not been used.

is it AA, or TC1 issue?

AA agent sometimes do not abide by the rules. they always insist a change of carrier of the same route requires reissuance of the ticket, which is wrong.
(e.g. ORD-LHR, you wanted to board a BA flight instead of AA. AA will make it very difficult, but BA/CX has no will just happily take the coupon)